The present invention is directed to a surface protection for the surfaces of parts of a hot-tinning system particularly the surface of hot air jets used in the process.
In a hot-tinning process, the excess solder is uniformly blown off of the treated work piece, for example, a printed circuit board by means of flow of hot air at a temperature of approximately 260.degree. C. that is directed by the assistance of air jets having slits or slots. Due to the air turbulence that occurs, the parts of the system coming into contact with the solder, particularly the slit jets become sprinkled or splattered with flux, dross, and tin dust. This spraying or sprinkling leads to an agressive deposit and finally to the blockage of the slit at the jet. In this case, the only alleviation of this condition is the cleaning of the jet.
Hitherto, the slit jets have been hard chromium plated and the guard rails as well as the solder frames were manufactured out of a stainless steel. These measures proved insufficient because the splattering or sprinkling particularly at the slit jets always occured due to the repeated work steps. The hard chromium plated surface of the slit jets were also attacked due to the long influence of these deposits and were partially destroyed. Therefore cleansing of the contaminated slit jets and other parts became necessary at shorter and shorter intervals. Cleaning of the machine parts particularly the slit jets involves a great outlay because the machine must be cooled off and then taken apart for the cleaning purposes. In addition, the hardened or solidified tin is not only difficult to remove from the lips of the slit jet, but the hard chromium plated layer is often removed over a long duration of the operation of the machine either due to the etching of the layer by flux or by alloying of the layer with other materials such as the solder.